On Tue, Oct 28, 2008 at 11:37:41AM +0100, Ingo Molnar (mingo@elte.hu) wrote:> What's your gut feeling, is that remaining small regression scheduler > or networking related?> > i'm cutting the ball in half and i'm passing over one half of it to > the networking folks, because your numbers show _huge_ sensitivity in > this workload, depending on networking settings:

Sorry for interrupting your conversation, Ingo, but before throwinga stone one should be clear himself, doesn't it? When you asked totest -tip tree and it was showed it regressed about 20 MB/s in mytest against the last tweaks you suggested, -tip still was merged and nowork on this issue was performed. Now previous tweaks (nohrticks andnobalalance, and although hrticks are now disabled, performance did notreturn to the vanilla .27 with tweaks) do not help anymore, soapparently there is additional problem.

So scheduler _does_ regress even right now when this thread is beingdiscussed.

Now let's return to the network. Ilpo Järvinen showed a nasty modulooperation in the fast path which David thinks on how to resolve it, butit happend that this change was introduced back in 2005, and althoughsome naive change allows to increase performance upto 370 MB/s, i.e. itgained us 2.5%, this was never accounted in previous changes.